In an air conditioning apparatus having an inside/outside air mode control function, the inside/outside air mode is automatically switched in accordance with a concentration of exhaust gas pollutants such as hydrocarbon (HC), CO carbon monoxide (CO) and nitrogen oxides (NOx) contained in an exhaust gas. This kind of air conditioning apparatus is for example disclosed in Unexamined Japanese Patent Publication No. JP-A-11-227444.
In the above air conditioning apparatus, the concentration of exhaust gas pollutants is monitored by a exhaust gas sensor mounted on a vehicle. The concentration is compared to a pollutant threshold that is preset in a controller of the air conditioning apparatus. The detected concentration is determined whether it is greater than the pollutant threshold. When the concentration is greater than the pollutant threshold, an inside/outside air mode is automatically switched to an inside air mode. Therefore, polluted outside air is not introduced in a passenger compartment.
Incidentally, particulate matter (PM) may be contained in the exhaust gas, in addition to the above exhaust gas components. However, it is difficult to detect the particulate matter by using the exhaust gas sensor. Even if a large amount of particulate matter is contained in the exhaust gas, when the concentration of the exhaust gas pollutants is low, the detected concentration will be lower than the pollutant threshold. In this case, an outside air mode is selected and maintained. As a result, the exhaust gas including the particulate matter is introduced in the passenger compartment.
Because the exhaust gas containing the particulate matter looks dirt, a user may recognize that the outside air is polluted. Even if the outside air looks dirt because of the particulate matter and the user desires the inside air mode, when the concentration of the exhaust gas pollutants is small, the outside air mode is selected and maintained. As a result, the outside air containing the particulate matter is introduced in the passenger compartment. Thus, it is difficult to control the inside/outside air mode as desired by the user.